A polymer electrolyte fuel cell causes a fuel gas, such as hydrogen, and an oxidizing gas, such as air, to electrochemically react with each other by a gas diffusion layer electrode including a catalyst layer, such as platinum, and generates electricity and heat at the same time. The configuration of the polymer electrolyte fuel cell is as follows. First, a catalyst layer is formed on each of both surfaces of a polymer electrolyte membrane which selectively transports hydrogen ions. The catalyst layer is formed by forming a catalyst body that is carbon powder supporting platinum based metal catalyst and mixing the catalyst body with hydrogen ion conductive polymer electrolyte. Next, a gas diffusion layer having fuel gas permeability and electron conductivity is formed on an outer surface of the catalyst layer. The gas diffusion layer is formed by, for example, carbon paper which is subjected to water repellent finish. A combination of the catalyst layer and the gas diffusion layer is called a gas diffusion electrode.
Next, a gas sealing material or a gasket is disposed on the circumference of the electrode with the polymer electrolyte membrane disposed therebetween so that the fuel gas for supplying fuel does not leak outside, and the fuel gas and the oxidizing gas do not mix with each other. The sealing material or the gasket is integrated with the electrode and the polymer electrolyte membrane, and this is called an MEA (membrane-electrode assembly). An electrically-conductive separator is disposed outside the MEA to mechanically fix the MEA and electrically connect the MEA with the adjacent MEA in series. On a portion of the separator which contacts the MEA, a gas passage is formed to supply a reactant gas to the electrode surface and carry away a produced gas and an excess gas. The gas passage may be formed separately from the separator. However, it is common to form a groove on the surface of the separator as the gas passage.
Many of the fuel cells have a laminated structure in which a large number of unit cells configured as above are stacked. At the time of the operation of the fuel cell, the heat generation occurs together with the electric power generation. In the laminated cell, by forming, for example, a cooling water passage for every 1-3 unit cells, it is possible to maintain the temperature of the cell constant, and at the same time, to utilize the generated heat energy in the form of, for example, hot water.
In the case of manufacturing a stack, the polymer electrolyte membrane is sandwiched between electrodes and further sandwiched between separators, and is fastened by end plates and bolts. It is necessary that the polymer electrolyte membrane have adequate strength to endure the fastening pressure and not to be physically damaged by abrasion, etc. in a long-term use. On the other hand, it is necessary to form the polymer electrolyte membrane as thin as possible to, for example, improve the proton conductivity. For these reasons, various studies have been made to increase the strength of the polymer electrolyte without increasing the thickness thereof.
For example, Patent Document 1 proposes the polymer electrolyte fuel cell which intends to prevent the polymer electrolyte membrane from damaging by attaching a frame-shaped protective film to a peripheral portion of the polymer electrolyte membrane (see FIG. 1 of Patent Document 1 for example). Hereinafter, the configuration of this polymer electrolyte fuel cell will be explained with reference to the drawings. FIG. 13 is an essential portion exploded perspective view for explaining a positional relation between a solid polymer electrolyte membrane and fluororesin sheets (protective films) in the polymer electrolyte fuel cell described in Patent Document 1. As shown in FIG. 13, in the polymer electrolyte fuel cell of Patent Document 1, a fluororesin sheet (protective film) 220 and a fluororesin sheet (protective film) 240 are disposed on a front main surface and a rear main surface of a solid polymer electrolyte membrane 1000, respectively, such that these sheets cover the entire peripheral portions of the substantially rectangular main surfaces of the solid polymer electrolyte membrane 1000.    Patent Document 1: Japanese Laid-Open Patent Application Publication 5-21077